Blankholder pinch indicator system for a power press

ABSTRACT

Blankholder pinch indicator system for a production power press where electrical or hydraulic means are utilized to sense the amount of clamping force applied at a number of positions about the edges of the workpiece being clamped thereby and visual indications of the clamping forces developed are produced at remote positions so that the press operator can maintain the proper amount of clamping force over successive press operating cycles.

I United States Patent 51 3,661,003 Heiberger et al. May 9, 1972 [54] BLANKHOLDER PINCH INDICATOR 1,844,250 2/1932 Hawkins ..72/351 SYSTEM FOR A POWER PRESS 1,891,121 12/1932 Thoreson 2,136,240 11/1938 Ernst 1 Inventors: Francis lieiberser, Elmhurst; Theodore 3,420,089 1/1969 Myers ..72/351 F. Novak, Oakbrook, both of 111.

[73] Assignee: Danly Machine Corporation, Chicago, 111. 'F Lanham Ass1slantExammer-E. M. Combs [22] Filed: Apr. 13, 1970 Attorney-Wolfe, Hubbard, Voit, Leydig & Osann, Ltd. [211 App]. No.: 27,897 ABSTRACT [52] Us. Cl 72/32 72/351 Blankholder pinch indicator system for a production power [51] Int Cl B2 d 22/00 press where electrical or hydraulic means are utilized to sense [58] Fieid Gi 3] 33 34 350 the amount of clamping force applied at a number of positions 5 about the edges of the workpiece being clamped thereby and visual indications of the clamping forces developed are [56] References Cited produced at remote positions so that the press operator can maintain the proper amount of clamping force over successive UNITED STATES PATENTS Press Operating y R22,163 8/ 1942 Ernst ..72/32 5 Claims, 7 Drawing Figures PATENTEDMAY 9 I972 3 661 003 SHEET 2 or 5 BLANKHOLDER PINCH INDICATOR SYSTEM FOR A POWER PRESS The present invention relates to power presses and more particularly to a system for indicating a proper and uniform blank holder loading on tonnage" application, for example, in terms of the percent of rated load, in double action presses to insure that the proper amount of clamping or blank holder pinch" occurs over successive press operating cycles.

In the conventional double action power press there is an inner slide which is reciprocatingly driven toward and away from the press base and a blank holder which surrounds the inner slide and is brought down to clamp a workpiece or blank about its edges while the inner slide, which carries a forming die, perfonns the work on the blank. In large drawing presses, such for example, those used in automotive production lines to manufacture a part such as an instrument panel, the workpiece starts out as a sheet or blank and must go through a series of pressing stages before emerging as the final product. The first press operation usually involves a double action type press to accomplish a very deep draw, the amount of which may vary in depth along the workpiece due to the stylized configuration of the part. Consequently, a press .blank holder must apply a sufficient amount of force or pinch about the edges of the blank, yet the force must be distributed as evenly and uniformly as possible to hold the edges during the drawing operation. Failure to do so can result in a pulling of a portion of the blank edge into the die cavity and the part must be scrapped.

It is therefore, a primary object of the present invention to provide a novel blank holder pinch indicator system for a production press which enables the desired pressure or pinch to be achieved with a high degree of accuracy and consistency, time after time, without use of wasteful trial and error procedures.

It is another object of the invention to provide a blank holder pinch indicating system, which, after initial adjustment, enables the correct blank holder clamping force or pinch to be reproduced automatically, thereby enabling consistent results in day by day operation of the power press, even by an unskilled and inexperienced operator and without wastage of blanks.

It is still another object to provide a blank holder pinch indicator system which gives a graphic display of the uniform application of the blank holder clamping force about the marginal edges of the blank, which is easily read and understood, and which may therefore be used by press operators with a high degree of confidence and reliability and without special instruction or training. In one of its aspects, it is an object of the invention to provide a blank holder pinch indicating system which gives a constant identification of uniform and even distribution of blank holder clamping force during the working portion ofthe cycle.

Finally, it is an object of the invention to provide a blank holder pinch indicating system which, in spite of its high sensitivity and accuracy, may be inexpensively constructed using readily available components of a noncritical nature, and which requires little or no maintainance over long periods of time, yet may easily be installed on presses of different sizes and different designs, either at the time of manufacture or on presses already in the field.

Other objects and advantages of the invention will become apparent after reading the attached detail description and upon reference to the drawings in which:

FIG. 1 is a perspective view of an exemplary double action, straight side press embodying a blank holder pinch indicating system of the present invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1 showing the disposition of one of the blank holder pinch sensing devices as employed in a press;

FIG. 3 is an enlarged side elevation view of a blank holder pinch indicator sensing device utilized with the present invention and showing the manner in which it is located in the press;

FIG. 4 is an enlarged sectional view of the sensing device illustrated in FIG. 3;

FIG. 5 is a view taken along the line 5-5 of FIG. 4 with parts broken away;

FIG. 6 is a schematic diagram of an electrical indicator arrangement in accordance with the present invention; and

FIG. 7 is a schematic diagram indicating a modified version of the present invention employing hydraulics;

While the invention has been described in connection with certain preferred embodiments, it will be understood that we do not intend to limit it to the embodiments shown, but intend to cover various modifications and alternative constructions and uses included within the spirit and scope of the invention.

Turning now to the drawings, there is illustrated in FIG. 1 one form of a double action straight side overdrive press with which the blank holder indicating system of the present invention can be used. The press indicated generally at 10, includes a pair of uprights 12, 14 extending from the bed I6 to the crown 18. The press inner slide (not shown) which carries a forming die in the present instance is mechanically reciprocated by a press crank or excentric 20 rotated by a press drive 22 for performing the shaping operation on a workpiece or blank. The blank holder 24 surrounds the inner slide and reciprocates vertically along suitable guides or ways provided on the inside of uprights 12, 14. The press drive through eccentrically mounted connecting rods or the like imparts oscillatory movement to crank and pitman arrangements indicated generally at 26 for example, there being four in number to produce the cycling of the blank holder 24 through a downward stroke, a clamping dwell period and an upward return stroke.

Referring to FIG. 2, it will be noted that the blank holder 24 is constructed of a frame, generally rectangular shaped, and for the present purposes it will suffice to say that the blank holder has a lower portion 27 to which is attached a bottom plate 28 and an upper portion 29 which is connected to lower portion 27 by means of fluid cylinders and piston arrangements to be more specifically described below. It should suffice to say at this point that the fluid arrangement serves to apply the requisite pressure for clamping the blank holder against the workpiece edges laying on the lower stationary die.

In order to drive the blank holder in a vertical reciprocating manner and apply at least some of the clamping force, the pitman arms 30, (FIG. 2, only one being shown) each located adjacent a corner of a blank holder are attached to a plunger 32 by a pin connection 34 with the plunger moving in guide 36. The ends of the plungers 32 engage screws 38 adjustably carried by pistons 40 located in the upper portion of the blank holder. The pistons 40 are sealingly contained within a cylinder portion 42 formed as a part of the blank holder lower portion structure such that a chamber 44 containing fluid under pressure is interposed between the piston 40 and the cylinder 42 portions of the blank holder. Thus, clamping force applied by pitman 30 to plunger 32 and in turn to screw 38 applies the force to the piston 40, which in turn exerts the pressure on the relatively moveable lower portion of the blank holder through the chamber 44 containing fluid under pressure. An overload valve (not shown) in the space generally indicated at 46 is provided in a fluid circuit with chamber 44; the valve being set for a predetermined pressure so that should the amount of force sought to be applied through the pitman 30 exceed prescribed limits, the fluid is released by the valve and the relative movement between piston 40 and chamber 42 relieves the excess pressure applied to the blankholder.

In order to provide for adjustment of the shut height of the blankholder, which shut height determines the extent of downward movement of blankholder 24 as well as a portion of the amount of blankholder pinch therewith, motor driven means (not shown) is utilized to move the screws 38 with respect to the plungers 32 and pistons 40. This adjustment is effected by providing nut couplings 48 between the plungers 32 and the pistons 40. Each of the nuts is in the form of a threaded worm wheel driven by corresponding worms. All of the nuts may be turned simultaneously by a single motor through suitable speed reducing angle drives and cross shafts (not shown).

In carrying out the present invention, a novel blankholder pinch indicator system is provided including an electrical sensing arrangement in the fonn of linear motion potentiometers 50 which are supplied from a DC source and meters coupled across the settings of the potentiometer sliders which may be calibrated directly in blankholder pinch as tonnage readings or applied pressure in other suitably selected designations. Thus, to this end as best shown by reference to FIGS. 2, 3 and 4 conjointly, the linear motion potentiometer 50 is interposed between piston 40 and the relatively moveable lower portion of the blankholder frame structure so that it is situated in a chamber 52 provided beneath the end of piston 40. For the purpose of mounting the linear motion potentiometer 50 a bracket 56 is provided with its upper flange and 58 attached to end 54 of piston 40 by bolt 60, or the like (FIG. 4).

Turning attention to the linear motion potentiometer commercially referred to as a Linipot", as illustrated in FIGS. 4 and 5, the resistance wire (FIG. 6) is carried in a casing 62 that is attached to a housing 64 mounted by bracket 66 to lower portion 27 of blank holder frame structure. For contacting the resistance wiring casing 62 a slider (FIG. 6) is carried by rod 70, which passes through the resistance wire casing 62 and is longitudinally moveable relative thereto. Opposite ends of the rod 70 are secured to generally U-shaped bracket 72, which has bent over ends 74 that are attached to a insulator member 76 by bolts 78. The insulator member 76 is moveable relative to housing 64 and in order to effect relative movements between the rod 70 and the resistance 62 there is provided a bolt 80 threadably attached to insulator member 76 at its threaded end and the opposite end is attached to flange 82 of bracket 56. An adjusting nut 84 carried by bolt 80 enables the relative position between rod 70 and'resistance 62 to be varied, such as for initial adjustment or for calibration purposes.

In accordance with the present invention, means are provided for assuring a visual indication of blank holder pinch at each of the four corners of the blank holder so that the press operator knows that at least the minimum required tonnage is applied about the marginal edges of the blank to prevent any edge from pulling loose while the inner slide effects the drawing operation. Consequently, as indicated in the schematic diagram, FIG. 6, each linear motion potentiometer (only one being shown) is connected across a regulated DC voltage source 86 and the wiper arm 70 of the potentiometer is connected directly to a meter 88 to indicate the blank holder tonnage applied. It will be appreciated that in actual practice there are four such meters 88 provided, one for each comer of the blank holder and the meters are disposed so as to be visible by the operator from his position at the press control panel.

In accordance with a further feature of the invention, means are provided for insuring a visual alert indication to an operator when the blank holder tonnage exceeds permissible amounts for the press in point. Thus, connected across the meter circuit there is provided a voltage level sensitive control 90 which is set to produce an electrical output signal such as necessary to light lamp 92 when the voltage level bypasses a predetermined amount. As will be apparent to one skilled in the art, the voltage level sensitive control 90 arranged to light lamp 72 may be set up to light the lamp when the blank holder tonnage applied is less than a predetermined minimum as well as when it exceeds a predetermined maximum or both indications may be provided for.

The calibration or setting of the meters 88 may be carried out so that the meters all have a zero" tonnage reading when the blank holder is stroked downward into contact with the workpiece and then adjustments may be made so that all the meters indicate at least the minimum required blank holder tonnage for a given workpiece when the pressure is applied on the blank holder to hold the workpiece.

The procedure for operation of the blank holder which establish the operating conditions for the pinch indicator may be briefly outlined as follows: The blank holder is stroked as previously indicated by pitmans 30 so that at the completion of the downstroke of the pitman, the blank holder bottom surface 28 engages a blank located on the lower die. Adjustment of the screws 38 through worm driven nut 48 may be made to produce a preloading on the blank by the blank holder when the pitmans reach the bottom of their stroke and the dwell period begins. Fluid pressure is then built up in the chamber 44 until it reaches a predetermined tonnage setting of the blank holder and the pressure is maintained during the entire dwell position. At the end of the dwell period the blank holder is stroked upwardly, at which time the fluid pressure to chamber 44 for effecting the requisite clamping force by the blank holder results in a relative displacement between piston 40 and the lower portion 27 of blank holder structure 24 which results in a change of position between the resistances and slides of linear motion potentiometers 50. The change of position of potentiometer 50 slides results in visual changes in meter readings and the operator can then view the tonnage applied at each of the four corners on meters 88. The press operator need be instructed only to make sure that the meters 88 all show a predetermined minumum tonnage application before the press slide is stroked.

Turning now to FIG. 7, there is shown a slightly modified form of blankholder pinch indicating system which is quite similar in operation to that shown in FIG. 6, but in the exemplary apparatus shown in FIG. 7, the fluid pressures developed during operation are utilized instead of the electrical means. To this end, there is schematically indicated the blankholder piston 40A upon which a load is applied with the piston being contained in the cylinder portion 42A, that includes chamber 44A supplied with fluid under pressure. For the purpose of supplying the fluid to the blankholder fluid cylinder chamber 44A, fluid is pumped from a source, (not shown) through inlet line 98 of overload valve 100, one such valve being provided for each of the blankholder force-applying connections. The overload valve piston 102 normally covers discharge port 104 so that as long as the pressure of the fluid in chamber 44A does not exceed a predetermined maximum, piston 102 is not displaced to such an extent that discharge port 104 is opened.

In keeping with the present form of the invention, the blank holder pinch indicating means is in the form of a pressure gauge 106, one such gauge being provided for each of the blankholder drive connections so that the press operator can view the indicated blankholder pinch at each corner directly on the gauges. The gauges 106 are interposed in a closed fluid circuit 108 maintained at a preset pressure by a constant pressure make up supply pump connected to inlet 110 through check valve 112. In order to insure that the circuit 108 is maintained filled with fluid without wide fluctuations in pressure such as before the makeup supply pump can cut in, accumulator 114 is interposed in circuit 108, In order to cause indication of the blankholder pinch by the pressure gauge, pressure changes in the blankholder cylinder chamber 44A and its inlet which cause a displacement of piston 102 which brings about an increase in the pressure in the control circuit 108. To this end, the piston 102 of valve 100 is formed with a camming surface 116 which acts upon a follower in the form of piston number 118 disposed in circuit .108. The arrangement is such that movement of the valve piston 102 to the right viewed in FIG. 7 cams the piston 118 upwardly, thereby increasing the pressure in circuit 108 with a consequent change in the gauge 106 reading.

Interposed also within the circuit 108 is a pressure operated switch 120 which is set to be actuated upon the occurrence of a predetermined pressure to monitor such devices as for example the fluid supply pump for circuit 108 and it will be appreciated by those skilled in the art that such a pressure switch can also be used to actuate other safety devices which prevent the overloading of press components.

We claim:

1. In a blankholder pinch indicator system for a power press having a moveable blankholder together with reciprocating driving means for adjusting the amount of force imposed by the blankholder in successive operating cycles, and said blankholder including fluid operated connection means adjacent each corner of the blankholder for applying a predetermined amount of clamping force therewith, the improvement comprising in combination, sensing means coupled to movable portions of each of said blankholder fluid force applying connection means for producing an output indicative of the linear movement of the blankholder fluid connections, means for transmitting the outputs of said sensing means to locations removed from said connection and visual indicator means connected to said transmitting means at the removed positions for producing a visual indication of blankholder pinch developed by the press blankholder adjacent each of the locations of applied pressure to the fluid connections.

2. A blankholder pinch indicator system as claimed in claim 1 wherein said fluid connection means includes relatively moveable piston and cylindermembers, said sensing means includes linear motion potentiometer for producing output signals according to the relative movement between said piston and cylinder portions and said visual indicator means includes meters for producing readings in response to variations in the output signals from respective ones of said potentiometers.

3. A blankholder pinch indicator system for a power press as claimed in claim 2 wherein said visual indicator means includes voltage sensitive control means for producing an electrical output signals when the outputs from said potentiometers exceeds predetermined amounts and lamps connected to the outputs of said voltage sensitive control means arranged to light lamps when the sensed output levels from said potentiometers reach the predetermined amounts.

4. A blankholder pinch indicator system for a power press as claimed in claim 1 wherein said sensing means include fluid circuit means including means for maintaining said circuits at a preset pressure, means responsive to relative movement between said piston and cylinder portions of the blankholder connections for varying the pressure in said circuit indicative of the forces applied by said blankholder connection and pressure gauges connected to said circuits for causing a visual indication of the blankholder pinch being applied by said blankholder.

5. A blankholder pinch indicator system as claimed in claim 4 wherein said fluid circuits include pressure operated switch means adapted to be actuated upon the presence of a predetermined pressure. 

1. In a blankholder pinch indicator system for a power press having a moveable blankholder together with reciprocating driving means for adjusting the amount of force imposed by the blankholder in successive operating cycles, and said blankholder including fluid operated connection means adjacent each corner of the blankholder for applying a predetermined amount of clamping force therewith, the improvement comprising in combination, sensing means coupled to movable portions of each of said blankholder fluid force applying connection means for producing an output indicative of the linear movement of the blankholder fluid connections, means for transmitting the outputs of said sensing means to locations removed from said connection and visual indicator means connected to said transmitting means at the removed positions for producing a visual indication of blankholder pinch developed by the press blankholder adjacent each of the locations of applied pressure to the fluid connections.
 2. A blankholder pinch indicator system as claimed in claim 1 wherein said fluid connection means includes relatively moveable piston and cylinder members, said sensing means includes linear motion potentiometer for producing output signals according to the relative movement between said piston and cylinder portions and said visual indicator means includes meters for producing readings in response to variations in the output signals from respective ones of said potentiometers.
 3. A blankholder pinch indicator system for a power press as claimed in claim 2 wherein said visual indicator means includes voltage sensitive control means for producing an electrical output signals when the outputs from said potentiometers exceeds predetermined amounts and lamps connected to the outputs of said voltage sensitive control means arranged to light lamps when the sensed output levels from said potentiometers reach the predetermined amounts.
 4. A blankholder pinch indicator system for a power press as claimed in claim 1 wherein said sensing means include fluid circuit means iNcluding means for maintaining said circuits at a preset pressure, means responsive to relative movement between said piston and cylinder portions of the blankholder connections for varying the pressure in said circuit indicative of the forces applied by said blankholder connection and pressure gauges connected to said circuits for causing a visual indication of the blankholder pinch being applied by said blankholder.
 5. A blankholder pinch indicator system as claimed in claim 4 wherein said fluid circuits include pressure operated switch means adapted to be actuated upon the presence of a predetermined pressure. 